The disclosure relates generally to glass chamfering methods, and more particularly to glass chamfering methods that utilize a laser in conjunction with mechanical finishing
No admission is made that any reference cited herein constitutes prior art. Applicant expressly reserves the right to challenge the accuracy and pertinence of any cited documents.
In all cases where glass panels are cut for applications in architectural, automotive, consumer electronics, to mention a few areas, there will be edges, which will very likely require attention. There are as many different methods to cut and separate glass. For example, glass can be cut mechanically (CNC machining, abrasive water jet, scribing and breaking, etc.), using electro-magnetic radiation (lasers, electrical discharges, gyrotron, etc). The more traditional and common methods (scribe and break with CNC machining) create edges that are populated with different types and sizes of defects. It is also common to find that the edges are not perfectly perpendicular to the surfaces. In order to eliminate the defects and give the edges a more even surface with improved strength, they are usually first ground, and then polished by a progression of polishing wheels, thus requiring multiple steps. This process involves abrasive removal of edge material that can give it the desired finishing and also shape its form (bull nosed, chamfered, pencil shape, etc). In order to allow for the grinding and the following polishing steps, it is necessary to cut parts that are larger than the final desired dimensions.
While it is well known and understood that eliminating defects will increase edge strength, there is not an agreement on the impact that shape has on edge strength. The confusion occurs mainly because it is well known that shape helps to increase damage resistance to impact and handling of the edges. The fact is that edge shape really does not determine edge strength as defined by resistance to flexural (or bending) forces, but the defects size and distribution do have a great impact. However, a shaped edge does help to improve impact resistance by creating smaller cross section and containing defects. For example, an edge with a straight face that is perpendicular to both surfaces accumulates stress at these right angled corners that will chip and break when it is impacted by another object. Because of the accumulated stress, the size of defects can be pretty big, which will diminish the strength of that edge considerably. On the other hand, due to its smoother shape, a rounded “bull-nosed” shaped edge will have lower accumulated stress and smaller cross section which helps to reduce the size and penetration of defects into the volume of the edge. Therefore, after an impact, a shaped edge should have higher “bending” strength than a flat edge.
For the reasons discussed above, it is often desirable to have the edges shaped, as opposed to flat and perpendicular to the surfaces. One important aspect of these mechanical cutting and edge shaping methods is the degree of maintenance of the machines. Both for cutting and grinding, old and worn down cutting heads or grinding rolls can produce damage which can significantly affect the strength of the edges, even if the naked eye cannot see the differences. Other issues with mechanical processing methods that require mechanical cutting, followed by mechanical grinding and the subsequent mechanical multiple polishing steps is that they are very labor intensive and require many grinding and polishing steps until the final desired finish, which generate a lot of debris and require cleaning steps to avoid introduction of damages to the surfaces.
Subsurface damage, as manifested by small microcracks and material modification (such as hackle and lateral checks) caused by any cutting process, is a concern because they diminish the edge strength of brittle materials, particularly glass. Mechanical and ablative laser processes are particularly problematic in this regard, because three processes can inflict layers of subsurface damage ranging from about 100-200 μm, or more in depth. Edges produced with conventional processing typically require a considerable amount of post-cut grinding and polishing to remove the subsurface damage layer(s).